Street or road # address, residential landline (tested before the sale), willingness to describe and measure the gun, patience with a paranoid's laundry list of questions about condition, a right of return with conditions stated up front; all help build a profile of a seller and his intentions. I doubt that asking for and probably paying for a condition report from an FFL holder whom you do not know promises much more than a second individual whose bona fides are also unknown. Feedback has helped me do some vetting at GB. A gazillion positive feedbacks means very little if there are also three to five negatives. A couple of those may be screwball buyers but probably not all. I've had the best luck with sellers with 10 to 20 sales of guns which indicate a specific area of interest and a more or less consistent quality and price level. Says the seller isn't a ragpicker or flea market recycler.
jack